Oestrogen receptors (ER) have classically been described as ligand-inducible nuclear transcription factors. The pleiotrophic effects of ER function have a predominant role in the direct regulation of the growth, differentiation and development of tissues of the human reproductive system. There are two ER subtypes, ER and ER which differ in their specificity for ligand and the consequent actions they orchestrate. Moreover, the latter exists in multiple splice variants of which ER is the only fully functional homologue. Research into the underlying differences in subtype responses to ligand has involved examination of the intranuclear dynamics of individual receptor subtypes. Studies into the mobility of ER in response to ligand have exclusively focused on studies of full length ER and ER independently in transfected cell lines. The studies described in this thesis have investigated the kinetics of ER using Fluorescence Recovery After Photobleaching (FRAP) in infected cell lines which lends itself to more precise expression of the subtype of interest. The morphological impact of natural oestrogenic and synthetic ligands on ERs was examined and the influence on the intranuclear dynamics assessed. Further to this, the effect of co-expression of different ER subtype combinations was examined. Studies on the intranuclear mobility of ER have confirmed and extended the findings of others. Previous work on the development of ER agonists and antagonists has been to target specific overexpressing ER subtypes in a physiological setting. In this study, we demonstrated for the first time an overwhelming ER -selective effect in slowing the rate of mobility within the nucleus, suggesting the study of intranuclear dynamics is an important parameter for the examination of efficacy of a compound. Differential responses to ligand based on co-infected partnerships indicate that heterodimerisation has a profound effect in augmenting ligand-dependent regulation and activity.